Cable and satellite television service providers utilize conditional access systems to broadcast encrypted information, representing programs, to authorized customers. Cable and satellite television service providers use a conditional access transmission system to encrypt signals so that access to the content of the signals is prevented except through a specified mechanism. Generally, cable and satellite television service providers supply set top boxes which can decrypt the signals transmitted by the cable and satellite television service providers. Each set top box can be configured to decrypt information from the cable and satellite television service providers on a per-service or per-event basis.
Many cable and satellite television service providers use the MPEG-2 encoding standard for transmission of encoded programs. MPEG-2 specifies a syntax for encoding video and audio information. It also specifies a transport stream format which allows multiple programs to be multiplexed into a single bit stream. The cable and satellite television service providers break down programs into elementary streams, for example video and audio, which are then encoded into packetized elementary streams (hereinafter “PES”) consisting of variable-length packets containing coded video and audio information. PES packets are then encapsulated in 188-byte transport packets for multiplexing and transmission. MPEG-2 specifies two stream formats for transmitting content: program stream and transport stream. Transport stream is used in broadcast environments.
An MPEG-2 transport stream consists of a stream of transport packets, each of which contains a packet identifier in the header. Packets sharing the same program identifier (hereinafter “PID”) are considered as belonging to the same stream. In this way, multiple independent streams can be carried in a transport stream or transport multiplex.
A set top box, provided by a particular cable or satellite television company, is configured to decrypt some or all of the individual streams carried within the transport stream sent by the particular cable or satellite television company. The set top box can be configured to decrypt transport streams on a per-service or per-event basis. The set top box generally will not work for another cable or satellite television company. If the user of the set top box elects to change from one cable or satellite television company to a second cable or satellite television company, the second cable or satellite television company must provide another set top box for the user.